A computer system, in particular, a small size computer system usually uses a spindle motor for rotational driving of a magnetic memory disk.
Such a spindle motor usually includes a rotor and a plurality of drive coils for giving revolution forces to the rotor.
The number of drive coils defines the number of excitation phases for making the rotor one cycle revolution. For example, a three phased spindle motor includes three drive coils. For making a rotor of the three phased spindle motor one cycle revolution, it needs to provide total six excitation phases.
The two coils among the three coils are excited at one excitation phase with shifting phases one by one in a predetermined successive order during the total six excitation phases in order to one cycle revolution drive of a rotor.
A conventional apparatus for controlling revolution drive of a spindle motor usually used a current control type apparatus.
FIG. 7 shows an example of such a current control type apparatus for controlling revolution drive of a spindle motor in which three motor drive signals U,V and W are provided to the respective three coils for making a rotor one cycle revolution.
As shown in this figure, it needs to provide a drive current signal in a full time of each excitation phase for making a coil excitation in a current control type apparatus.
In this type apparatus, these motor drive signals are supplied through a current control circuit and a current supply circuit which are provided between a source voltage and the coils in serial. The current control circuit controls an amount of a constant drive current so as to change its value in response to a detected revolution speed of a motor.
Namely, the conventional apparatus achieves a stable revolution drive of a spindle motor by changing a value of a constant current for exciting a full time of a phase in accordance with a revolution state of a motor.
However, since the current control circuit is provided between the power source and the drive coils in serial, the current control circuit itself wastes a power of and it causes to drop down the source voltage due to a wasting power loss in the current control circuit.
Consequently, it is impossible to use the power source voltage efficiently for supplying a drive current to the respective coils.
This is a serious problem, in particular, for a small size computer system since it usually uses a battery source for driving a magnetic memory disk.
In order to avoid such a wasting power loss of the source voltage, it is proposed to provide a chopper control type motor control apparatus for making revolution control of a spindle motor.
The chopper control type motor control apparatus uses a pulse wave moduration signal (hereinafter refers to "PWM signal") for driving a motor as shown in FIG. 8. for exciting a coil in a exciting phase.
As shown in the figure, the value amount of the respective motor drive signals is maintained at a maximum value of the source voltage Vcc since the power source is directly coupled to the respective coils.
Namely, the PWM signal controls an on/off operation of the source voltage at a maximum value with a certain PWM-duty (B/A) cycle.
The on/off duty cycle of the PWM signal changes in accordance with a detected revolution speed of a spindle motor. Namely, the chopper control type motor control apparatus artificially adjusts an amount of a drive current by an on/off switching operation of the source voltage directly for eliminating a power loss in a current control circuit.
However, the chopper control type motor control apparatus also has anther serious problem of switching noises. Since the source voltage is frequently on/off switching at the maximum value with a short period, it causes to produce big noises.
Since read/write operations to a magnetic disk is done by a small value signal, switching noises are also a serious problem for a small size computer. It causes to make an error operation of a reading data or a writing data.
As mentioned, the conventional current control type motor drive apparatus has a defect of wasting consumption of a power source and the chopper control type motor drive apparatus also has a serious problem of switching noises.
Accordingly, it is an object of the invention to provide a new apparatus and method for controlling revolution drive of a motor of an efficient use of a power source.
It is another object of this invention to provide a new apparatus and method for controlling a revolution drive of a motor of a low switch noise.
It is another object of this invention to provide a new apparatus and method for controlling revolution drive of a spindle motor which can eliminate a waste loss consumption of a power source and also can decrease an influence of a switching noise during a small signal operation.
It is still another object of this invention to provide a PWM exciting phase synchronous control type apparatus for controlling revolution drive of a spindle motor which can achieve an efficient use a power source and also can decrease an influence of the noises due to the PWM switching operation during a read/write operation.
It is still further object of this invention to provide a PWM exciting phase synchronous control type apparatus for achieving revolution drive of a spindle motor which can adjust an amount of a drive current by changing a PWM duty in an exciting phase without appearing a switching noise.
It is still more object of this invention to provide an apparatus and method for controlling motor revolution which can minimize spike noises during a read/write mode operation.
It is still more object of this invention to provide an apparatus and method for controlling motor revolution which can change a drive mode in order to minimize spike noises during a read/write operation and also to reduce the power consumption during another operation.